https://bayescourse.netlify.app/libs/anchor-sections-1.0.1/anchor-sections.js

1// Anchor sections v1.0 written by Atsushi Yasumoto on Oct 3rd, 2020.
2document.addEventListener('DOMContentLoaded', function() {
3  // Do nothing if AnchorJS is used
4  if (typeof window.anchors === 'object' && anchors.hasOwnProperty('hasAnchorJSLink')) {
5    return;
6  }
7
8  const h = document.querySelectorAll('h1, h2, h3, h4, h5, h6');
9
10  // Do nothing if sections are already anchored
11  if (Array.from(h).some(x => x.classList.contains('hasAnchor'))) {
12    return null;
13  }
14
15  // Use section id when pandoc runs with --section-divs
16  const section_id = function(x) {
17    return ((x.classList.contains('section') || (x.tagName === 'SECTION'))
18            ? x.id : '');
19  };
20
21  // Add anchors
22  h.forEach(function(x) {
23    const id = x.id || section_id(x.parentElement);
24    if (id === '' || x.matches(':empty')) {
25      return null;
26    }
27    let anchor = document.createElement('a');
28    anchor.href = '#' + id;
29    anchor.classList = ['anchor-section'];
30    x.classList.add('hasAnchor');
31    x.appendChild(anchor);
32  });
33});